The present invention relates to loudness meters for displaying various aspects of loudness of audio signals.
The loudness of a music track or radio/TV program is one of the most important perceptual properties of the sound. Therefore loudness meters are often employed at different stages of broadcast and music production. A loudness meter can measure (i.e. estimate) one or more types of loudness of an audio signal, and display the loudness estimates or levels. By reading the loudness meter, the producer or audio engineer can get an impression of the loudness without having to spend the time listening for the duration of each program.
Advanced loudness meters can display both the current loudness and its ‘history’, that is, the previous loudness estimates. An example of such a loudness meter is shown in FIG. 1 (prior art).
In an audio production, some kind of audio processor is normally employed to continuously control/adjust the ‘volume’, loudness, or spectral/dynamic balance of the sound. Such processors may be known as dynamic-range compressors, limiters, automatic loudness controllers, multiband compressors, dynamic equalizers, loudness maximizers, exciters, etc.
It is common practice to meter the loudness and history at the output of such an audio processor. Thereby the audio engineer will be able to monitor and control the loudness resulting from the processing, by means of numerical and/or graphical representations of various loudness measures. For instance, it could be verified whether certain loudness measures are compliant with the technical standards and recommendations that applies to different fields of audio production.
In some cases, it may be useful to monitor the loudness at the input as well as at the output of an audio processor, or of a chain of multiple audio processors. A setup like that would allow the engineer to inspect the effective changes made by the processor(s), as well as the resulting loudness.
However, in order to establish such a metering setup, the engineer would have to employ two individual loudness meters, which may be impractical, clumsy, and uneconomic. Furthermore, to be able to compare the displays on these two meters, every measurement- and display-parameter of the meters would carefully have to be set up identically. Even then, it might be inconvenient to accurately compare the displays of the two meters, as it would involve reading the two separate displays.
When a new type of program or audio signal begins the meters would typically need to be reset, in order to clear the level history and null the filter states, signal buffers etc. In a two-meter setup, such a reset operation would need to be manually performed on both meters—as close in time as possible to each other—in order not to skew their relative time base.